The present invention relates to a configuration of a radio equipment capable of changing antenna directivity on real time basis, and particularly to a configuration of a radio equipment used in an adaptive array radio base station.
Recently, various methods of transmission channel allocation have been proposed to realize effective use of frequency, in a mobile communication system, of which some have been practically implemented.
FIG. 30 shows an arrangement of channels in various communication systems including frequency division multiple access (FDMA), time division multiple access (TDMA) and path division multiple access (PDMA).
Referring to FIG. 30, FDMA, TDMA and PDMA will be briefly described. FIG. 30(a) represents FDMA in which analog signals of users 1 to 4 are subjected to frequency division and transmitted over radio waves of different frequencies f1 to f4, and the signals of respective users 1 to 4 are separated by frequency filters.
In TDMA shown in FIG. 30(b), digitized signals of respective users are transmitted over the radio waves having different frequencies f1 to f4 and time-divided time slot by time slot (time slot: a prescribed time period), and the signals of respective users are separated by the frequency filters and time-synchronization between a base station and mobile terminals of respective users.
Recently, PDMA method has been proposed to improve efficiency of use of radio frequency, as portable telephones have come to be widely used. In the PDMA method, one time slot of one frequency is spatially divided to enable transmission of data of a plurality of users, as shown in FIG. 30(c). In the PDMA, signals of respective users are separated by the frequency filters, the time synchronization between the base station and the mobile terminals of respective users, and a mutual interference eliminating apparatus such as an adaptive array.
The operation principle of such an adaptive array radio base station is described in the following literature, for example:
B. Widrow, et al.: xe2x80x9cAdaptive Antenna Systemsxe2x80x9d, Proc. IEEE, vol.55, No.12, pp.2143-2159 (December 1967).
S. P. Applebaum: xe2x80x9cAdaptive Arraysxe2x80x9d, IEEE Trans. Antennas and Propag., vol.AP-24, No.5, pp.585-598 (September 1976).
O. L. Frost, III: xe2x80x9cAdaptive Least Squares Optimization Subject to Linear Equality Constraintsxe2x80x9d, SEL-70-055, Technical Report, No.6796-2, Information System Lab., Stanford Univ. (August 1970).
B. Widrow and S. D. Stearns: xe2x80x9cAdaptive Signal Processingxe2x80x9d, Prentice-Hall, Englewood Cliffs (1985).
R. A. Monzingo and T. W. Miller: xe2x80x9cIntroduction to Adaptive Arraysxe2x80x9d, John Wiley and Sons, New York (1980).
J. E. Hudson: xe2x80x9cAdaptive Array Principlesxe2x80x9d, Peter Peregrinus Ltd., London (1981).
R. T. Compton, Jr.: xe2x80x9cAdaptive Antennasxe2x80x94Concepts and Performancexe2x80x9d, Prentice-Hall, Englewood Cliffs (1988).
E. Nicolau and D. Zaharia: xe2x80x9cAdaptive Arraysxe2x80x9d, Elsevier, Amsterdam (1989).
FIG. 31 is a model diagram conceptually showing the operation principle of such an adaptive array radio base station. Referring to FIG. 31, an adaptive array radio base station 1 includes an array antenna 2 formed by n antennas #1, #2, #3, . . . , #n, and a first hatched area 3 shows a range in which radio waves from the array antenna 2 can be received. A second hatched area 7 shows a range in which radio waves from adjacent another radio base station 6 can be received.
In the area 3, the adaptive array radio base station 1 transmits/receives a radio signal to/from a portable telephone 4 forming a terminal of a user A (arrow 5). In the area 7, the radio base station 6 transmits/receives a radio signal to/from a portable telephone 8 forming a terminal of another user B (arrow 9).
When the radio signal for the portable telephone 4 of the user A happens to be equal in frequency to the radio signal for the portable telephone 8 of the user B, it follows that the radio signal from the portable telephone 8 of the user B serves as an unnecessary interference signal in the area 3 depending on the position of the user B, to disadvantageously mix into the radio signal transmitted between the portable telephone 4 of the user A and the adaptive array radio base station 1.
In this case, it follows that the adaptive array radio base station 1 receiving the mixed radio signals from both users A and B in the aforementioned manner outputs the signals from the users A and B in a mixed state unless some necessary processing is performed, to disadvantageously hinder communication with the regular user A.
[Configuration and Operation of Conventional Adaptive Array Antenna]
In order to eliminate the signal from the user B from the output signal, the adaptive array radio base station 1 performs the following processing. FIG. 32 is a schematic block diagram showing the configuration of the adaptive array radio base station 1.
Assuming that A(t) represents the signal from the user A and B(t) represents the signal from the user B, a signal x1(t) received in the first antenna #1 forming the array antenna 2 shown in FIG. 31 is expressed as follows:
x1(t)=a1xc3x97A(t)+b1xc3x97B(t)
where a1 and b1 represent coefficients changing in real time, as described later.
A signal x2(t) received in the second antenna #2 is expressed as follows:
x2(t)=a2xc3x97A(t)+b2xc3x97B(t)
where a2 and b2 also represent coefficients changing in real time.
A signal x3(t) received in the third antenna #3 is expressed as follows:
x3(t)=a3xc3x97A(t)+b3xc3x97B(t)
where a3 and b3 also represent coefficients changing in real time.
Similarly, a signal xn(t) received in the n-th antenna #n is expressed as follows:
xn(t)=anxc3x97A(t)+bnxc3x97B(t)
where an and bn also represent coefficients changing in real time.
The above coefficients a1, a2, a3, . . . , an show that the antennas #1, #2, #3, . . . , #n forming the array antenna 2 are different in receiving strength from each other with respect to the radio signal from the user A since the relative positions of the antennas #1, #2, #3, . . . , #n are different from each other (the antennas #1, #2, #3, . . . , #n are arranged at intervals about five times the wavelength of the radio signal, i.e., about 1 m, from each other).
The above coefficients b1, b2, b3, . . . , bn also show that the antennas #1, #2, #3, . . . , #n are different in receiving strength from each other with respect to the radio signal from the user B. The users A and B are moving and hence these coefficients a1, a2, a3, an and b1, b2, b3, . . . , bn change in real time.
The signals x1(t), x2(t), x3(t), . . . , xn(t) received in the respective antennas #1, #2, #3, . . . , #n are input to a receiving unit 1R forming the adaptive array radio base station 1 through corresponding switches 10-1, 10-2, 10-3, . . . , 10-n respectively so that the received signals are supplied to a weight vector control unit 11 and to one input of each of the corresponding multipliers 12-1, 12-2, 12-3, . . . , 12-n respectively.
Weights w1, w2, w3, . . . , wn for the signals x1(t), x2(t), x3(t), . . . , xn(t) received in the antennas #1, #2, #3, . . . , #n are applied from the weight vector control unit 11 to other inputs of these multipliers 12-1, 12-2, 12-3, . . . , 12-n respectively. The weight vector control unit 11 calculates these weights w1, w2, w3, . . . , wn in real time, as described later.
Therefore, the signal x1(t) received in the antenna #1 is converted to w1xc3x97(a1A(t)+b1B(t)) through the multiplier 12-1, the signal x2(t) received in the antenna #2 is converted to w2xc3x97(a2A(t)+b2B(t)) through the multiplier 12-2, the signal x3(t) received in the antenna #3 is converted to w3xc3x97(a3A(t)+b3B(t)) through the multiplier 12-3, and the signal xn(t) received in the antenna #n is converted to wnxc3x97(anA(t)+bnB(t)) through the multiplier 12-n.
An adder 13 adds the outputs of these multipliers 12-1, 12-2, 12-3, . . . , 12-n, and outputs the following signal:
w1(a1A(t)+b1B(t))+w2(a2A(t)+b2B(t))+w3(a3A(t)+b3B(t))+ . . . +wn(anA(t)+bnB(t))
This expression is classified into terms related to the signals A(t) and B(t) respectively as follows:
(w1a1+w2a2+w3a3+ . . . +wnan)A(t)+(w1b1+w2b2+w3b3+ . . . +wnbn)B(t)
As described later, the adaptive array radio base station 1 identifies the users A and B and calculates the aforementioned weights w1, w2, w3, . . . , wn to be capable of extracting only the signal from the desired user. Referring to FIG. 32, for example, the weight vector control unit 11 regards the coefficients a1, a2, a3, . . . , an and b1, b2, b3, . . . , bn as constants and calculates the weights w1, w2, w3, . . . , wn so that the coefficients of the signals A(t) and B(t) are 1 and 0 as a whole respectively, in order to extract only the signal A(t) from the intended user A for communication.
In other words, the weight vector control unit 11 solves the following simultaneous linear equations, thereby calculating the weights w1, w2, w3, . . . , wn on real time basis so that the coefficients of the signals A(t) and B(t) are 1 and 0 respectively:
w1a1+w2a2+w3a3+ . . . +wnan=1
w1b1+w2b2+w3b3+ . . . +wnbn=0
The method of solving the above simultaneous linear equations, not described in this specification, is known as described in the aforementioned literature and already put into practice in an actual adaptive array radio base station.
When setting the weights w1, w2, w3, . . . , wn in the aforementioned manner, the adder 13 outputs the following signal:
output signal=1xc3x97A(t)+0xc3x97B(t)=A(t)
[User Identification, Training Signal]
The aforementioned users A and B are identified as follows:
FIG. 33 is a schematic diagram showing the frame structure of a radio signal for a portable telephone set. The radio signal for the portable telephone set is roughly formed by a preamble consisting of a signal sequence known to the radio base station and data (sound etc.) consisting of a signal sequence unknown to the radio base station.
The signal sequence of the preamble includes a signal sequence of information for recognizing whether or not the user is a desired user for making communication with the radio base station. The weight vector control unit 11 (FIG. 32) of the adaptive array radio base station 1 compares a training signal corresponding to the user A fetched from a memory 14 with the received signal sequence and performs weight vector control (decision of weights) for extracting a signal apparently including the signal sequence corresponding to the user A. The adaptive array radio base station 1 outputs the signal from the user A extracted in the aforementioned manner as an output signal SRX(t).
Referring again to FIG. 32, an external input signal STX(t) is input to a transmission unit 1T forming the adaptive array radio base station 1 and supplied to one input of each of multipliers 15-1, 15-2, 15-3, . . . , 15-n. The weights w1, w2, w3, . . . , wn previously calculated by the weight vector control unit 11 on the basis of the received signal are copied and applied to other inputs of these multipliers 15-1, 15-2, 15-3, . . . , 15-n respectively.
The input signals STX(t) weighted by these multipliers 15-1, 15-2, 15-3, . . . , 15-n are sent to the corresponding antennas #1, #2, #3, . . . , #n through corresponding switches 10-1, 10-2, 10-3, . . . , 10-n respectively, and transmitted into the area 3 shown in FIG. 31.
The signal transmitted through the same array antenna 2 as that in receiving is weighted for the target user A similarly to the received signal, and hence the portable telephone set 4 of the user A receives the transmitted radio signal as if the signal has directivity to the user A. FIG. 34 images such transfer of a radio signal between the user A and the adaptive array radio base station 1. Imaged is such a state that the adaptive array radio base station 1 transmits the radio signal with directivity toward the target portable telephone set 4 of the user A as shown in a virtual area 3a in FIG. 34 in contrast with the area 3 of FIG. 31 showing the range actually receiving radio waves.
As described above, in the PDMA method, a technique is necessary to remove co-channel interference. In this point, an adaptive array that places nulls on the interfering waves adaptively is an effective means, as it can effectively suppress the interfering wave even when the level of the interfering wave is higher than the level of the desired wave.
When an adaptive array is used for a base station, it becomes possible not only to remove interference at the time of reception but also to reduce unnecessary radiation at the time of transmission.
At this time, an array pattern at the time of transmission may be an array pattern for reception, or the array pattern may be newly generated based on a result of incoming direction estimation, for example. The latter method is applicable no matter whether FDD (Frequency Division Duplex) or TDD (Time Division Duplex) is used. It requires, however, a complicated process. When the former approach is to be used while FDD is utilized, modification of the array arrangement or weight becomes necessary, as the array patterns for transmission and reception are different. Therefore, generally, application is on the premise that TDD is utilized, and in an environment where external slots are continuous, satisfactory characteristic has been ensured.
As described above, in the TDD/PDMA method using an adaptive array in the base station, when an array pattern (weight vector pattern) obtained for the up link is used for the down link, transmission directivity may possibly be degraded in the down link because of time difference between the up and down links, assuming a dynamic Rayleigh propagation degree with angular spread.
More specifically, there is a time interval from transmission of the radiowave from a user terminal to the base station through the up link until radiowave is emitted from the base station to the user terminal through the down link. Therefore, if the speed of movement of the user terminal is not negligible, transmission directivity degrades because of the difference between the direction of radiowave emission from the base station and the actual direction of the user terminal.
As a method of estimating weight for the down link considering such a variation in the propagation path, a method of performing first order extrapolation utilizing a weight vector value obtained in the up link has been proposed in the following articles.
(1) Kato, Ohgane, Ogawa, Itoh, Proc. of the Institute of Electronics, Information and Communication Engineers (B-II), vol. J81-B-II, No. 1, pp. 1-9, January 1998.
(2) Doi, Ohgane, Karasawa, Technical Report of the Institute of Electronics, Information and Communication Engineers, RCS97-68, pp.27-32, July 1997.
However, when time change of the weight is actually monitored, it is not linear, and therefore, the conventional method utilizing the first order extrapolation of the weight vector results in a large error.
The present invention was made to solve the above described problem, and an object is to provide a radio equipment in which, based on the finding that weight of the adaptive array can be uniquely represented by the response vector of each antenna element, time change of the response vector is estimated so as to indirectly estimate the weight, whereby degradation of error rate in the down link generated from time difference between up and down links can be suppressed even in the TDD/PDMA systems, assuming a dynamic Rayleigh propagation path with angular spread.
The present invention provides a radio equipment changing antenna directivity on real time basis and transmitting/receiving signals to/from a plurality of terminals by time division of the signal into a plurality of slots, including: a plurality of antennas arranged in a discrete manner; and a transmission circuit and a reception circuit sharing the plurality of antennas for transmitting/receiving signals; wherein the reception circuit includes a reception signal separating circuit for separating a signal from a specific terminal among the plurality of terminals, based on signals from the plurality of antennas, when a reception signal is received, and a reception propagation path estimating circuit estimating a propagation path from the specific terminal based on signals from the plurality of antennas, when the reception signal is received; the transmission circuit includes a transmission propagation path estimating circuit predicting a propagation path when a transmission signal is transmitted, based on a result of estimation by the reception propagation path estimating circuit, and a transmission directivity control circuit updating the antenna directivity when the transmission signal is transmitted, based on the result of estimation by the transmission propagation path estimating circuit; wherein each slot includes a first data area of a first prescribed size provided in the slot so as to distinguish transmission/reception to/from the specific terminal, and a second data area of a second prescribed size provided in an area succeeding and apart by a prescribed interval from the first data area, in the slot to distinguish transmission/reception to/from the specific terminal; the reception propagation path estimating circuit provides the first estimation value and a second estimation value of the specific terminal based on data in the first and second data areas, respectively; and the transmission propagation path estimating circuit predicts propagation path when the transmission signal is transmitted, by extrapolating the first and second estimation values.
The radio equipment corresponds to the configuration of the radio equipment as described above and, in addition, the first data area includes a first training data area, and the second data area includes a second training data area.
The radio equipment corresponds to the configuration of the radio equipment as described above, and in addition, the first training data area is provided at a head of the slot, and the second training data area is provided at a tail of the slot.
The radio equipment corresponds to the configuration of the radio equipment as described above, and in addition, the reception propagation path estimating circuit provides a first reception coefficient vector and a second reception coefficient vector corresponding to an impulse response of the specific terminal of the propagation path from the specific terminal, based on the data of the first and second training data areas, respectively.
The radio equipment corresponds to the configuration of the radio equipment as described above, and in addition, the reception propagation path estimating circuit provides the first reception coefficient vector and the second reception coefficient vector, by ensemble average of each of the signals received by the plurality of antennas and a signal from the specific terminal separated by the reception signal separating circuit.
The present invention provides a radio equipment changing antenna directivity on real time basis and transmitting/receiving signals to/from a plurality of terminals by time division of the signal into a plurality of slots, including: a plurality of antennas arranged in a discrete manner; and a transmission circuit and a reception circuit sharing the plurality of antennas for transmitting/receiving signals; wherein the reception circuit includes a reception signal separating circuit for separating a signal from a specific terminal among the plurality of terminals, based on signals from the plurality of antennas, when a reception signal is received, and a reception propagation path estimating circuit estimating a propagation path from the specific terminal based on signals from the plurality of antennas, when the reception signal is received; the transmission circuit includes a transmission propagation path estimating circuit predicting a propagation path when a transmission signal is transmitted, based on a result of estimation by the reception propagation path estimating circuit, and a transmission directivity control circuit updating the antenna directivity when the transmission signal is transmitted, based on the result of estimation by the transmission propagation path estimating circuit; wherein each slot includes a training data area provided within the slot and having a prescribed number of training data, and a data area provided successive to the training data area and having a plurality of data each representing information to be transmitted/received; the reception propagation path estimating circuit provides a first estimation value and a second estimation value of the propagation path from the specific terminal, based on data of the training data area and the data area, respectively; and the transmission propagation path estimating circuit predicts propagation path when the transmission signal is transmitted, by extrapolation of the first and second estimation values.
The radio equipment corresponds to the configuration of the radio equipment as described above, and in addition, the training data area is provided at a head of the slot.
The radio equipment corresponds to the configuration of the radio equipment as described two paragraphs above, and in addition, the reception propagation path estimating circuit successively provides a first reception coefficient vector and a second reception coefficient vector corresponding to impulse response of the specific terminal of the propagation path from the specific terminal, based on a plurality of data in the training data area and the data area.
The radio equipment corresponds to the configuration of the radio equipment as described above, and in addition, the first reception coefficient vector and the reception coefficient vector are successively derived by steepest descent method.
The radio equipment corresponds to the configuration of the radio equipment as described two paragraphs above, and in addition the first reception coefficient vector and the second reception coefficient vector are successively derived by recursive least square method.
The present invention provides a radio equipment changing antenna directivity on real time basis and transmitting/receiving signals to/from a plurality of terminals by time division of the signal into a plurality of slots, including a plurality of antennas arranged in a discrete manner; and a transmission circuit and a reception circuit sharing the plurality of antennas for transmitting/receiving signals; wherein the reception circuit includes a reception signal separating circuit for separating a signal from a specific terminal among the plurality of terminals, based on signals from the plurality of antennas, when a reception signal is received, and a reception propagation path estimating circuit estimating a propagation path from the specific terminal based on signals from the plurality of antennas, when the reception signal is received; the transmission circuit includes a transmission propagation path estimating circuit predicting a propagation path when a transmission signal is transmitted, based on a result of estimation by the reception propagation path estimating circuit, and a transmission directivity control circuit updating the antenna directivity when the transmission signal is transmitted, based on the result of estimation by the transmission propagation path estimating circuit; wherein each slot includes a training data area provided within the slot and having a prescribed number of training data, and a data area provided successive to the training data area and having a plurality of data each representing information to be transmitted/received; the reception propagation path estimating circuit provides a plurality of estimation values of the propagation path from the specific terminal, based on the data of the training data area and the data area, respectively; and the transmission propagation path estimating circuit regresses the plurality of estimation values and predicts propagation path when the transmission signal is transmitted, by extrapolation based on a result of regression.
The radio equipment corresponds to the configuration of the radio equipment as described above, wherein the training data area is provided at a head of the slot.
The radio equipment corresponds to the configuration of the radio equipment as described two paragraphs above, and in addition, the reception transmission path estimating circuit successively provides a plurality of reception coefficient vectors corresponding to impulse response from the specific terminal of the propagation path from the specific terminal, based on a plurality of data in the training data area and the data area.
The radio equipment corresponds to the configuration of the radio equipment as described above and in addition, the plurality of reception coefficient vectors are successively provided by steepest descent method.
The radio equipment corresponds to the configuration of the radio equipment as described two paragraphs above, and in addition, the plurality of reception coefficient vectors are successively provided by recursive least square method.
The radio equipment corresponds to the configuration of the radio equipment as described in the first paragraph of this section, and in addition, the reception signal separating circuit includes a reception weight vector calculating unit receiving reception signals from the plurality of antennas and providing, on real time basis, a reception weight vector for separating a signal from the specific terminal, a plurality of first multipliers each receiving at one input reception signals from the plurality of antennas respectively, and receiving corresponding element of the reception weight vector respectively at the other input, and an adder adding signals from the plurality of multipliers; and the transmission directivity control circuit includes a transmission weight vector calculating unit providing a transmission weight vector based on a result of estimation from the transmission propagation path estimating circuit, and a plurality of second multipliers each receiving at one input a transmission signal, and receiving the transmission weight vector at the other input and applying to the plurality of antennas respectively.
The present invention provides a radio equipment changing antenna directivity on real time basis and transmitting/receiving signals time divisionally to/from a plurality of terminals, including: a plurality of antennas arranged in a discrete manner; and a transmission circuit and a reception circuit sharing the plurality of antennas for transmitting/receiving signals; wherein the reception circuit includes a reception signal separating circuit for separating a signal from a specific terminal among the plurality of terminals, based on signals from the plurality of antennas, when a reception signal is received, and a reception propagation path estimating circuit estimating a propagation path from the specific terminal based on signals from the plurality of antennas, when the reception signal is received; the transmission circuit includes a transmission propagation path estimating circuit predicting a propagation path when a transmission signal is transmitted, based on a result of estimation by the reception propagation path estimating circuit, and a transmission directivity control circuit updating the antenna directivity when the transmission signal is transmitted, based on the result of estimation by the transmission propagation path estimating circuit; wherein the reception signal separating circuit includes a reception weight vector calculating unit receiving reception signals from the plurality of antennas and providing, on real time basis, a reception weight vector for separating a signal from the specific terminal, a plurality of first multipliers each receiving at one input the reception signals from the plurality of antennas respectively and receiving corresponding element of the reception weight vector at the other input, and an adder adding signals from the plurality of multipliers; the transmission directivity control circuit includes a moving speed determining unit determining speed of movement of the specific terminal based on a result of estimation by the reception propagation path estimating circuit, a transmission weight vector calculating unit providing a transmission weight vector based on a result of estimation by the transmission propagation path estimating circuit, a switching circuit receiving the transmission weight vector and the reception weight vector, and selectively outputting in accordance with a result of determination by the moving speed determining unit, and a plurality of second multipliers receiving at one input a transmission signal and receiving an output of the switching circuit at the other input respectively, and applying to the plurality of antennas, respectively.
The present invention provides a radio equipment changing antenna directivity on real time basis and transmitting/receiving signals time divisionally to/from a plurality of terminals, including: a plurality of antennas arranged in a discrete manner; and a transmission circuit and a reception circuit sharing the plurality of antennas for transmitting/receiving signals; wherein the reception circuit includes a reception signal separating circuit for separating a signal from a specific terminal among the plurality of terminals, based on signals from the plurality of antennas, when a reception signal is received, and a reception propagation path estimating circuit estimating a propagation path from the specific terminal based on signals from the plurality of antennas, when the reception signal is received; the transmission circuit includes a transmission propagation path estimating circuit predicting a propagation path when a transmission signal is transmitted, based on a result of estimation by the reception propagation path estimating circuit, and a transmission directivity control circuit updating the antenna directivity when the transmission signal is transmitted, based on the result of estimation by the transmission propagation path estimating circuit; wherein the reception signal separating circuit includes a reception weight vector calculating unit receiving reception signals from the plurality of antennas and providing, on real time basis, a reception weight vector for separating a signal from the specific terminal, a reception signal level operating unit receiving the reception signals from the plurality of antennas and providing a reception level of the signal from the specific terminal, a plurality of first multipliers receiving at an input the reception signals from the plurality of antennas respectively, and receiving corresponding elements of the reception weight vector at the other input respectively, and an adder adding the signals from the plurality of multiplying units; and the transmission directivity control circuit includes a reception signal level determining unit determining a reception signal level of the specific terminal based on a result of operation of the reception signal level operating unit, a transmission weight vector calculating unit providing a transmission weight vector based on a result of estimation by the transmission propagation path estimating circuit, a switching circuit receiving the transmission weight vector and the reception weight vector and selectively outputting in accordance with a result of determination by the reception signal level determining unit, and a plurality of multipliers receiving at one input the transmission signal and receiving an output of the switching circuit at the other input respectively, and providing to the plurality of antennas, respectively.